We've seen smartphone breathalysers before, some exclusive to iPhones and some that work on iOS and Android. The thing is that these are generally rather large and expensive. DrinkMate on the other hand is a different story, it's an Android breathalyser that is small, cheap, and draws power from the phone's micro USB port.
It works the same as any other mobile breathalyser, you simply blow into the device and it'll display your blood alcohol level (BAC) using a companion app. The developers are claiming that the prototype is accurate to +/- 0.01% of your true BAC, but the device only registers up to 0.2% BAC. Then again, if you're that drunk in the first place you definitely shouldn't be driving anyway.
There are bound to be a number of pitfalls to this type of thing, such as testing yourself too soon after having a drink, but the companion app is specifically designed to navigate these issues and ensure that people are using the device correctly.
Android fragmentation does inevitably bring up the problem of compatibility issues (especially with older handsets), but DrinkMate has provided a list of phones that are guaranteed to work -- as well as phones that should work but have yet to be tested by the development team. In theory DrinkMate should work on any fairly recent high-end Android handset.
DrinkMate is currently looking for backing on Kickstarter, and a $33 pledge (£20, including shipping) will get you a device of your own sometime in December. If the campaign is successful (and it looks like it will be) the team will begin work on a version of the DrinkMate for the iPhone. [Kickstarter via TechCrunch]